CTF3: Design of Driving Beam Combiner Ring

Proceedings of …, 2010

The probe beam Linac, CALIFES, of the CLIC Test Facility (CTF3) has been developed by CEA Saclay, LAL Orsay and CERN to deliver trains of short bunches (0.75 ps) spaced by 0.667 ns at an energy around 170 MeV with a charge of 0.6 nC to the TBTS (Two-beam Test Stand) intended to test the high gradient CLIC 12 GHz accelerating structures. Based on 3 former LEP Injector Linac (LIL) accelerating structures and on a newly developed RF photo-injector, the whole accelerator is powered with a single 3 GHz klystron delivering pulses of 45 MW during 5.5 μs to a RF pulse compression cavity and a network of waveguides, splitters, phase-shifters and an attenuator. We relate here results collected during the various commissioning and operation periods which gave stable beam characteristics delivered to the TBTS with performances close to nominal. Progress has been made in the laser system to improve the beam charge and stability, in the space charge compensation to optimize the emittance, in RF pulse shape for energy and energy spread. The installation of a specially developed RF power phase shifter for the first accelerating structure used in velocity bunching allows the control of the bunch length.

Proc. EPAC, 2004

The aim of the CLIC (Compact Linear Collider) Study is to investigate the feasibility of a high luminosity, multi-TeV linear e+e-collider. CLIC is based on a two-beam method, in which a high current drive beam is decelerated to produce 30 GHz RF power needed for high-gradient acceleration of the main beam running parallel to it. To demonstrate the outstanding feasibility issues of the scheme a new CLIC Test Facility, CTF3, is being constructed at CERN by an international collaboration. In its final configuration CTF3 will consist of a 150 MeV drive beam linac followed by a 42 m long delay loop and an 84 m combiner ring. The installation will include a 30 GHz high power test stand, a representative CLIC module and a test decelerator. The first part of the linac was installed and commissioned with beam in 2003. The first issue addressed was the generation and acceleration of a high-current drive beam in the "full beam loading" condition where RF power is converted into beam power with an efficiency of more than 90 %. The full beam loading operation was successfully demonstrated with the nominal beam current of 3.5 A. A variety of beam measurements have been performed, showing good agreement with expectations.

Physical Review Special …, 2011

2006

The CLIC Test Facility CTF3, built at CERN by an international collaboration, aims at demonstrating the feasibility of the CLIC scheme of multi-TeV electronpositron linear collider by 2010. In particular, one of the main goals is to study the generation of high-current electron pulses by interleaving bunch trains in delay lines and rings using transverse RF deflectors. This will be done in the 42 m long delay loop, built under the responsibility of INFN/LNF, and the 84 m long combiner ring that will follow it. The delay loop installation was completed and its commissioning started at the end of 2005. In this paper the commissioning results are presented, including the first tests of beam recombination.

The CLIC Drive Beam Recombination Complex (DBRC) is designed to compress beam pulses from a current of 4 A to 100 A before using them to produce RF power in the deceleration lines. The beam is transported isochronously through a complex system consisting of a delay loop, two combiner rings and final turn around. The system is designed to preserve transverse and longitudinal emittances. During the optics design, chromaticity and non-linear dispersion were identified as the main single particle dynamics causes for transverse emittance growth. Different sextupole families are used to compensate these chromatic effects while keeping isochronicity. The bunch length is also adjusted to minimize coherent synchrotron radiation effects on bunch length, energy spread and transverse emittance. Finally, the injection scheme of the combiner rings was improved by making the time-variable bump created with help of the RF deflectors truly achromatic.

2009

Abstract The aim of the CLIC Test Facility CTF3, built at CERN by an international collaboration, is to address the main feasibility issues of the CLIC electron-positron linear collider technology by 2010. One key-issue studied at CTF3 is the generation of the very high current drive beam, used in CLIC as the RF power source.

In order to demonstrate the feasibility of the CLIC multi-TeV linear collider option, the drive beam complex at the CLIC Test Facility (CTF3) at CERN is providing highcurrent electron pulses for a number of related experiments. By means of a system of electron pulse compression and bunch frequency multiplication, a fully loaded, 120 MeV linac is used to generate 140 ns electron pulses of around 28 Amperes. Subsequent deceleration of this high-current drive beam demonstrates principles behind the CLIC acceleration scheme, and produces 12 GHz RF power for experimental purposes. As the facility has progressed toward routine operation, a number of studies aimed at improving the drive beam performance have been carried out. Additional feedbacks, automated steering programs, and improved control of optics and dispersion have contributed to a more stable, reproducible drive beam with consequent benefits for the experiments.

The proposed Compact Linear Collider (CLIC) is based on a two-beam acceleration scheme. The energy needed to accelerate a low intensity "main" beam is provided by a high intensity, low energy "drive" beam. The precision and stability of the phase relation between two beams is crucial for the performance of the scheme. The tolerable phase jitter is 0.2 deg rms at 12 GHz. For this reason it is fundamental to understand the main possible causes of the drive beam timing jitter. Experimental work aimed at such understanding was done in the CLIC Test Facility (CTF3) where a drive beam with characteristics similar to the CLIC one is produced. Several phase measurements allowed us to conclude that the main source of phase jitter is energy jitter of the beam transformed and amplified into phase jitter when passing through a magnetic chicane. This conclusion is supported by measurements done with different momentum compaction values in the chicane. In this paper the results of these several phase measurements will be presented and compared with expectations.

Abstract The objective of the CLIC Test Facility CTF3 is to demonstrate the feasibility issues of the CLIC two-beam technology. CTF3 consists of an electron linac followed by a delay loop, a combiner ring and a two-beam test area. One issue studied in CTF3 is the efficient generation of a very high current drive beam, used in CLIC as the power source to accelerate the main beam to multi-TeV energies.

2008

The CLIC project based on the innovative Two Beams Acceleration concept is currently under study at CTF3 where the acceleration of a probe beam will be demonstrated. This paper will describe in details the status of the probe beam linac called CALIFES. This linac (170 MeV, 0.9 A) is developed by CEA Saclay, LAL Orsay and CERN. It has been installed in the new experimental area of CTF3 to deliver short bunches (1.8 ps) with a charge of 0.6 nC to the CLIC 12 GHz accelerating structures. We report new results of beam dynamic and RF simulations considering the new CLIC parameters. The construction of CALIFES in the CLEX building is presented. Recent measurements from the laser system are discussed. Details about the HV modulator tests and the power phase shifter fabrication will be described and the start of commissioning will be also reported.